Why does Morgan support Endogenous Pacemakers?
Effects of endogenous pacemakers and exogenic zeitgebers
Fractional median resetting responses of the circadian phase-shifting effect in response to 3 cycles of exposure to 2 different regimen of 5 h intermittent bright-light stimuli on the output of the endogenous circadian pacemaker. The relative duration of bright-light exposure for each nominal 5-h stimulus represents the percentage of the 5-h episode that subjects were exposed to bright light in each of the intermittent light groups. The response fractions represent the ratios of the resetting responses observed in the endogenous circadian rhythm of core body temperature in each of the intermittent light groups (solid black bars) to the resetting response of subjects in the continuous light group. The response fractions predicted by the direct-drive model of the effect of the bright light on the endogenous circadian pacemaker for the intermittent light conditions are plotted in open bars ().
What is the main endogenous pacemaker for the sleep-wake cycle?
Lighting regimen used to study the phase-shifting effect of 3 cycles of 5-h bright-light exposures on the endogenous circadian pacemaker. Exposures were centered 1.5 h after the endogenous circadian core body temperature minimum (time 0 on axis) to induce phase advances of the endogenous circadian pacemaker (a). Each stimulus consisted of exposure to either 3 cycles of 5 h of continuous bright (∼10,000 lx) light (100% stimulus;b), 3 cycles of 5 h of bright light consisting of ∼46 min of light within each 90-min duty cycle (63% stiumulus;c), 3 cycles of 5 h of bright light consisting of ∼5.3 min of bright light within each 25-min duty cycle (31% stimulus; d), or complete darkness (0% stimulus;e). Each 5-h stimulus was preceded and followed by 25-min transitions during which the intensities were increased and decreased in 5-min intervals. Similarly, within the 90- and 25-min duty cycles, light intensities were progressively increased and decreased in 1-min intervals and 10-s intervals, respectively. The effective duration of bright-light exposure producing drive on the endogenous pacemaker for all transitions are represented by the dashed lines ().